1. Field of the Invention
The present invention relates to an ink jet head substrate capable of performing stable printing with reduced malfunctions with respect to noises, an ink jet head using this ink jet head substrate, and an ink jet print apparatus such as a printer using this ink jet head.
2. Related Background Art
An ink jet recording method (liquid jet recording method) is extremely excellent, for example, in that generation of noises at the time of operation is negligibly very small and that high-speed recording is possible and recording on so-called plain paper can be performed without requiring special processing of fixing. Thus, the ink jet recording method has become a mainstream of a print system recently. In particular, in an ink jet head utilizing thermal energy, thermal energy generated by a heating element (electrothermal converting element; heater) is given to a liquid, whereby a foaming phenomenon is selectively caused in the liquid, and ink liquid droplets are discharged from discharge ports by energy of the foaming. In such an ink jet head, for improvement of recording density (resolution), a large number of fine heating elements are arranged on a silicon semiconductor substrate and discharge ports are further arranged so as to be opposed to the heating elements, respectively. In addition, a drive circuit and peripheral circuits for driving the heating elements are also provided on the silicon semiconductor substrate. The silicon semiconductor substrate with the heating elements, the drive circuit, and the peripheral circuits provided thereon in this way is called an ink jet head substrate. For example, there is a tendency to provide, within an identical silicon semiconductor substrate, several tens to several thousands of heating elements, drivers corresponding to each of the heating elements, a shift register with the same number of bits as the number of heating elements for sending respective image data, which are inputted serially, to the drivers in parallel with each other, and a latch circuit for temporarily storing data, which are outputted from the shift register, for each heating element.
As described above, recently, integration of logic circuits such as a driver, a shift register, and a latch on a head substrate has been advanced. However, a current pulse flowing to one heating element instantaneously reaches a relatively high current value and, in the case in which the number of heating elements to be simultaneously turned ON (i.e., the number of discharge ports from which ink droplets are simultaneously discharged) is large, for example, a pulse-like current in the order of one to several amperes flows to a power supply line for driving the heating elements and a ground (GND) line.
Since such a pulse-like large current flows, there arises such a fear that the logic circuit section on the head substrate malfunctions due to noises caused by inductive coupling generated in flexible wiring from a printer apparatus main body to an ink jet head, wiring in the ink jet head, or the like. In addition, radiation of unnecessary electromagnetic noises to the outside of the printer apparatus is also concerned.
A level of inductive noises becomes higher as an amount of change of current per a unit time increases. Thus, as the number of discharge ports provided in the ink jet head is increased for high-speed or high-precision printing or the like, it is expected that the number of elements which are simultaneously turned ON increases and a current value of current pulses further increases as well. Accordingly, a noise level becomes higher.
Therefore, instead of driving the large number of discharge ports provided on the head substrate simultaneously, these discharge ports are divided into a plurality of blocks, and driving by a unit of block is performed. That is, at certain timing, the heating elements are selectively driven in a first block and no heating element is driven in the remaining blocks. At the next timing, the heating elements are selectively driven in a second block and no heating element is driven in the remaining blocks. The heating elements in subsequent blocks are driven in the same manner, whereby driving of the heating elements corresponding to all the discharge ports is completed once.
However, in the case in which there are a large number of discharge ports, a magnitude of a current pulse cannot be reduced simply by dividing the discharge ports into an appropriate number of blocks, and an amount of generation of inductive noises cannot be suppressed. It is also possible that the number of heating elements which are simultaneously turned ON is reduced by increasing the number of blocks. However, in such a case, there is a fear in that a time allocated to one block is reduced and sufficient energy for ink discharge cannot be obtained.
Thus, U.S. Pat. No. 6,243,111 discloses a configuration for shifting a drive pulse, which is applied to heating elements belonging to an identical block, little by little for each heating element. That is, in forming an ink jet head substrate, a hysteresis circuit is provided in an input section together with components for a logic discharge control circuit such as heating elements, a driver, and a shift register and, at the same time, a CR (capacitor resistor) integrating circuit is formed in a signal path for a heat pulse (input pulse width signal), which regulates a pulse width and timing of a drive pulse, such that the drive pulse is applied to different heating elements at staggered timing. Consequently, the heat pulse is delayed to drive the respective heating elements sequentially. In this way, timing of the heat pulse is staggered using the CR integrating circuit, and a current flowing to the heating elements is controlled, whereby the number of heating elements which are turned ON at exactly the same timing is reduced, and a peak value of a current or a rising ratio of a current due to the drive pulse is reduced to suppress generation of noises. Consequently, even if there is increase in the number of heating elements which are driven simultaneously due to increase in the number of discharge ports or high-density implementation of discharge ports indispensable for high-speed printing, generation of inductive noises or the like can be suppressed.
However, in the case in which generation of noises is suppressed by using the CR integrating circuit as disclosed in U.S. Pat. No. 6,243,111, if there are fluctuations in C (capacitance) and R (resistance), a product of the fluctuations results in a fluctuation in a delay value of the heat pulse. Thus, a current flowing to the heating elements cannot be controlled with high accuracy and, as a result, generation of noises cannot be suppressed sufficiently. In addition, since the CR integrating circuit is constituted by an input buffer, a capacitor, and a resistor, when a difference of a wiring pattern length to a logic circuit input of the next stage increases, the delay value fluctuates. In addition, in the head substrate which is typically manufactured using a silicon semiconductor device manufacturing technique, a gate oxide film is often used for a capacitor and a diffused resistor is often used as a resistor. When it is intended to constitute a CR integrating circuit having a desired time constant, the capacitor and the resistor occupy a large area on the head substrate, and the head substrate is enlarged.
Therefore, it is an object of the present invention to provide an ink jet head substrate which can sufficiently suppress generation of noises and can be constituted small in size, an ink jet head using such a substrate, and an ink jet print apparatus.